This invention relates to a sharpening apparatus for sharpening the cutter elements and grinding the rakers of a chain saw chain. Chain saws in general include a chain guide bar on which is mounted a saw chain having a plurality of cutting elements or teeth whose cutting edges are inclined with respect to the direction of the movement of the saw chain and which are undercut or raked at a predetermined angle. Such chain cutting elements must be sharpened relatively frequently and the rakers periodically ground to maintain maximum cutting efficiency of the saw. Hand sharpening of a chain is both time consuming and furthermore will not generally result in optimum cutting edges since it requires a great deal of skill on the part of the operator to properly sharpen a chain and few people possess such skill. Additionally there is a tendency, when hand sharpening a chain, to remove too much material from the cutting teeth of the chain, thereby reducing the life of the chain.
Saw chain grinding machines have been provided in the prior art for sharpening saw chains but these machines have had a number of disadvantages. In many of these machines the chain must be removed from the saw bar and mounted on a special holder on the grinder, clamped in the holder, and adjusted with respect to the grinding wheel before the grinding operation can proceed. Then, after grinding, the chain must be removed from the special holder and remounted and readjusted on the saw bar. All of those operations add up to a very time consuming operation.
Prior art grinding machines also are generally designed for commercial establishments and therefore tend to be relatively heavy and difficult to move. The chain saw operator must therefore remove the saw chain and take it to a commercial establishment for sharpening. It is therefore necessary for an operator to have several chains available to avoid lost production time.
A further disadvantage of the prior art machines is that they have been relatively complicated and difficult to adjust. Quite often a saw operator will hand sharpen a chain several times before bringing the chain in to a sharpening establishment to be ground. Because of the inability to control the hand sharpening process, and the resulting non-uniform cutting edges, commercial establishments attempt to make the cutting elements uniform in length and will grind off a substantial amount from the cutting edges of the teeth to insure that all the teeth are of equal size. Thus, much material is usually removed from the teeth in such operations, thereby shortening the life of the chain.
Still other prior art grinding machines have been provided which mount directly on the saw bar and therefore are more portable than the above referred to types of commercial grinding machines. A disadvantage of these bar mounted types of grinding machines is that they are rather difficult to adjust and use and therefore will not generally result in optimum sharpening of the chain. In most of these devices the grinding machine has to be dismounted, remounted and adjusted to grind the opposite set of cutter teeth of the saw chain. It is therefore desired to provide a chain sharpening apparatus whereby the chain can be ground in situ on the bar, which is simple to use and adjust, and whereby the grinding apparatus can be used to grind both the right hand and left hand teeth of the chain by a simple repositioning of the grinding apparatus motor and grind wheel assembly without readjustment of the grinding machine. It is also desired to provide such a sharpening apparatus which may be used to accurately grind the rakers of the teeth. It is furthermore desired to provide such an apparatus having a simple index mechanism to control the amount of material to be removed from the individual saw teeth.
In one prior art patent, U.S. Pat. No. 3,877,324, a grinding apparatus is provided for grinding a saw chain in situ wherein the saw is mounted on the grinding apparatus with the saw bar in a clamping device and the saw motor supported on a support table. The teeth on one side of the chain are first sharpened whereafter the entire saw will be rotated with respect to the central vertical axis on which the grinding wheel and motor is mounted for grinding the teeth on the other side of the chain. This sharpening apparatus, while preferable over the other prior art chain saw sharpening devices, has the disadvantage of being relatively complicated and bulky and difficult to adjust.